Its open source. You can extend it it's functionality with zimlets and it's already quite popular with universities.

http://www.zimbra.com/

Why aren't they simply blocking google using robots.txt if they don't want to be listed?

Another thing to look at is that both the EU and the US also do software patents. Isn't it wonderful. Occasional anti-trust lawsuits which don't work followed by ramming software patents down everyone's throats.